1. Field of the Invention
The present invention pertains to the art of cooking appliances and, more particularly, to a cooking appliance having an automated calibration system that maintains operational parameters of the cooking appliance within optimal limits.
2. Discussion of the Prior Art
In general, it is known that electric cooking appliances are affected by variations in supply voltage. That is, as electric cooking appliances utilize electric heating elements that output power, variations in supply voltage will result in variations in power output. Given that P=V2/R, a ten-volt variation in voltage will result in a significantly greater variation in power output by the electric heating element. In cooking appliances, variations in supply voltage can alter the time it takes to achieve a desired cooking temperature. In addition, variations in supply voltages make maintaining a desired temperature more difficult. When the cooking appliance is not operating under optimal conditions, pre-established operating parameters will not be able to achieve or maintain desired output conditions. Food could end up being either over or under-cooked. For example, when operating an electric cooking appliance that is programmed with a cook time, the established cook time may not be sufficient to properly cook the food if significant voltage variations occur during the cooking operation. Based thereon, it is considered important to periodically calibrate or adjust the operational parameters to correspond to the amount of heat produced by the electric elements.
In recognition of this problem, the prior art contains several examples of systems designed to compensate for variations in supply voltage. Some of these systems monitor the supply voltage and, based on the monitored voltage, alter an overall cook time for a cooking operation. Other systems monitor the supply voltage, then compare the supply voltage with a known, nominal value. The difference, if any, between the supply voltage and the known value is used to set particular cycle times of one or more electric heating elements. In still other systems, a controller monitors power and voltage values. These values are compared to stored data to determine particular cycle times of a heating element. While each of the above systems is generally effective, they fail to account for other factors which can influence power output by an electric heating element.
In addition to supply voltage variations, the resistance of an electric heating element will change over time. A change in resistance of the element will also have an effect on the amount of power output by the element. Also, the degradation of insulation around the cooking appliance and door sealing characteristics will affect the amount of heat needed to maintain a particular temperature within an appliance. None of the examples proposed in the prior art address these issues. In addition, the prior art systems are not considered to be readily adaptable to new oven designs.
Based on the above, there still exists a need in the art for an oven calibration system that will effectively maintain an oven temperature regardless of variations in supply voltage. More specifically, there exists a need for an oven calibration system that will also account for changes in oven performance resulting from ordinary wear of the cooking appliance in order to remain within optimal operating conditions.